The present invention relates to a device for reducing pulsation developed in a variable displacement compressor.
When the variable displacement compressor is operating with a low flow rate of refrigerant gas, pulsation of suction refrigerant gas is developed due to self-excited vibration of a suction valve of the compressor. Pulsation propagated out of the compressor may cause large vibration and noise. Various methods for reducing such pulsation are proposed. According to the methods, the effective area of the suction passage located upstream of the suction valve is controlled so as to reduce pressure fluctuation developed during operation of the compressor with a low flow rate of the refrigerant gas.
The Japanese Unexamined Patent Application Publication No. 2000-136776 or the first reference discloses a variable displacement compressor having a device for reducing pulsation of suction refrigerant gas. The compressor has a suction chamber and a suction port which communicate with each other through a gas passage. A valve chamber is provided between the gas passage and the suction port. An opening control valve is disposed vertically movably in the valve chamber for controlling the opening of the gas passage. The control valve is operable to change the opening of the gas passage in accordance with the flow rate of suction refrigerant gas. When the compressor is operating with a low flow rate of suction refrigerant gas, the pulsation of the suction refrigerant gas that is due to self-excited vibration of a suction valve of the compressor is reduced.
Specifically, a spring is disposed in the valve chamber for urging the control valve toward the suction port. The control valve is vertically movable by the pressure difference between the suction chamber and the suction port. The control valve is so arranged that the opening of the gas passage becomes maximum when the control valve is at the lowest position thereof and minimum when the control valve is at the highest position thereof. The valve chamber communicates with the suction chamber through a communication hole and also with the suction port through a hole formed in the control valve.
When the compressor is operating with a low flow rate of suction refrigerant gas, the control valve moves upward due to a small pressure difference between the suction chamber and the suction port and the opening of the gas passage is reduced, accordingly. In this case, part of the refrigerant gas at the suction port flows into the valve chamber through the hole of the control valve and then into the suction chamber through the communication hole. The pulsation of refrigerant gas developed during operation of the compressor with a low flow rate of refrigerant gas is rectified while the pulsation is propagated from the suction chamber to the suction port through the communication hole, the valve chamber and the hole of the control valve, so that noise is not developed. That is, the propagation of pressure fluctuation is reduced due to the sound deadening effect of the suction chamber having a large volume and the throttling effect of the hole of the control valve.
The Japanese Unexamined Patent Application Publication No. 2006-207484 or the second reference also discloses a variable displacement compressor having a device for reducing pulsation of suction refrigerant gas. The compressor has a suction chamber and a suction port which communicate with each other through a suction passage. A muffler is provided in the suction passage for reducing the pulsation of suction refrigerant gas. An opening control valve is provided upstream of the muffler for controlling the opening of the suction passage. The control valve has a valve chamber, a cylindrical valve body having a bottom at one end thereof, a cylindrical movable body having a bottom at one end thereof and a spring. The valve body and the movable body are movably disposed in the valve chamber. The spring is provided between the valve body and the movable body. A stop is provided in the inner wall of the valve chamber for restricting movement of the valve body. Another stop is also provided in the inner wall of the valve chamber for restricting movement of the movable body. A suction hole is formed between the valve chamber and the muffler. Suction pressure acts on the surface of the valve body adjacent to the suction port in the direction which causes the suction hole to be opened. Crank chamber pressure acts on the surface of the movable body adjacent to the bottom of the valve chamber through the communication passage in the direction which causes the suction hole to be closed.
When the compressor is operating with a low flow rate of suction refrigerant gas, the crank chamber pressure exceeds the suction pressure, so that the valve body and the movable body are moved while compressing the spring in the valve chamber in the direction which causes the suction hole to be closed. In the state where the movable body is in contact with the stop, the valve body is urged toward the suction port by the spring to reduce the opening of the suction hole to an extent that it is slightly opened, so that the sound deadening effect of the muffler is achieved thereby to reduce the pressure fluctuation. In addition, hermetically closing the space between the valve body and the movable body, damping effect is achieved thereby to prevent development of the noise that is due to the vibration of the valve body caused by the pulsation of suction refrigerant gas.
When the compressor of the first reference is operating with a low flow rate of suction refrigerant gas, the device for reducing pulsation of the compressor achieves the sound deadening effect developed between the suction chamber, the gas passage and the suction port by throttling the gas passage by the control valve. In addition, because the valve chamber communicates with the suction chamber and the suction port through the communication hole and the hole of the control valve, respectively, the device of the compressor achieves the sound deadening effect developed between the suction chamber, the communication hole, the valve chamber, the hole of the control valve and the suction port. However, the pulsation developed during operation of the compressor with a low flow rate of refrigerant gas cannot be reduced merely by the aforementioned sound deadening effects.
The device for reducing pulsation of the compressor of the second reference has the muffler in the suction passage. When the compressor is operating with a low flow rate of suction refrigerant gas, the suction hole of the muffler is throttled by the valve body of the control valve so as to achieve substantial sound deadening effect. However, providing the muffler in the compressor causes an increase of the size of the compressor, which makes it difficult to install a compressor in a limited space such as a vehicle engine room. The effect of pulsation reduction achieved by the provision of the muffler is not sufficient to compensate for the disadvantage of increased size of the compressor due to the provision of the muffler.
The present invention is directed to a device for reducing pulsation in a variable displacement compressor which is simplified and sufficiently achieves the effect for reducing the pulsation developed during operation of the compressor with a low flow rate of refrigerant gas without increasing the size of the compressor.